New Series S, can’t add Xbox 360 Profile

Hello

I bought a new Series S (already own X) for my son to play. His favourite game is Crazy Taxi, but when loading the game, it asks me to download my Xbox 360 profile. Selecting Download shows the attached error.

Same game works fine on my X and my 360 account is added with the same gamertag as my Xbox One account.

I've looked this up and from the results, have tried, without success:

Connecting console to mobile hot-spot from phone

Setting manual port to anything starting with 5

Setting DNS to 8.8.8.8 and 8.8.4.4

Disabling all account security except mobile phone and password

Adding a second account to the S and launching the game on there

NAT type is Open.

Clearing local Xbox 360 storage

Factory reset console

I've messaged Xbox Support but their AI suggests I remove the account, but obviously can't do that.

Would appreciate any help.

Thank you!